(CNSNews.com) – Less than two weeks before stringent new U.S. and European Union sanctions targeting Tehran are due to go into effect, Iran’s negotiators on Monday tied any concession on its part to “sanctions relief.” That reinforces the already low expectations that multilateral talks in Moscow may achieve a breakthrough in the decade-long standoff.

Representatives of the United States, Russia, China, Britain, France and Germany (P5+1) are holding two days of talks with the Iranians in the Russian capital, chaired by European Union foreign policy chief Catherine Ashton, seeking Iran’s agreement to stop enriching uranium to 19.75 percent purity.

Enrichment to 3.5 percent is the grade required to fuel a power plant, but Iran in 2010 began enriching uranium to 19.75 percent, the upper end of the required level for research reactors like its Tehran-based medical research facility.

Although weapons-grade uranium is enriched at more than 90 percent, experts say the journey from 3.5 to 19.75 percent requires considerably more work than does the one from 19.75 to 90 percent. Iran consistently denies its nuclear program has a military end-goal, as strongly suspected by Western governments.

The Institute for Science and International Security said in a report Friday that, at its present pace, Iran would have enough 19.75 percent-enriched uranium – if further enriched to weapons-grade – for a nuclear weapon by early next year. If it picked up the pace, that point could be reached by the end of 2012, ISIS said.

At the last P5+1 talks, in Baghdad last month, Iran was made an offer. According to Iranian reports, it included fuel for the Tehran plant and an easing of sanctions, in return for Iran ending the 19.75 percent enrichment, closing the underground Fordow facility near Qom where the work is taking place, and shipping its stockpile of 19.75 percent-enriched uranium out of the country.

Iran made its own demands in Baghdad, including official recognition of Iran’s right to enrich uranium.

In Moscow on Monday, Iran’s chief negotiator Saeed Jalili pressed again for that recognition, as well as relief from international sanctions.

Ashton spokesman Michael Mann told reporters the Iranians had responded to the P5+1 Baghdad proposals, but had also raised “lots of questions and well-known positions, including past grievances.”

Mann described the talks as “an intense and tough exchange of views, while Jalili’s deputy, Ali Baqeri, called them “serious and constructive.” In Washington, State Department spokeswoman Victoria Nuland said the U.S. agreed with the E.U. characterization.

Forty-four U.S. senators from both parties signed a letter to President Obama on Friday, urging him to stop negotiating with Tehran altogether unless it agrees at this week’s talks immediately to take the steps proposed in the P5+1 Baghdad package – stop all enrichment above five percent, shut down the Fordow facility, and ship all uranium enriched above five percent out of the country.

“On the other hand, if the sessions in Moscow produce no substantive agreement, we urge you to reevaluate the utility of further talks at this time and instead focus on significantly increasing the pressure on the Iranian government through sanctions and making clear that a credible military option exists,” the senators wrote.

U.S. sanctions, E.U. embargo loom

Iran’s currency has plummeted in value since the beginning of the year while food and other prices have risen sharply. Income from oil exports is down, as customers look for alternative suppliers in order to avoid impending sanctions.

From June 28, the U.S. will impose sanctions on foreign financial institutions that do business with Iran’s central bank, which deals with oil transactions.

Ahead of that deadline, Secretary of State Hillary Clinton last week announced that seven Iranian customers – India, Malaysia, South Africa, South Korea, Sri Lanka, Turkey and Taiwan – had “significantly reduced their volume of crude oil purchases from Iran,” and on that basis would be exempt from the looming sanctions. Last March she made a similar determination with regard to Japan and 10 European countries.

According to U.S. Energy Information Administration data for the first half of 2011, Iran’s top ten oil customers were, in order, China, Japan, India, South Korea, Italy, Turkey, Spain, South Africa, France and Sri Lanka.

Clinton’s determinations apply to every one of those countries bar China, which has repeatedly defended its business with Iran and stressed its opposition to unilateral sanctions.

Even China, however, has begun to diversify, increasing purchases from sources including Saudi Arabia and Russia, according to industry figures. Still, unless the Obama administration grants Beijing a waiver before next Thursday, sanctions against applicable Chinese institutions will begin.

The situation promises to get even more difficult for Iran after July 1, when an E.U. embargo on Iranian crude oil takes effect.

On the eve of the Moscow talks, President Mahmoud Ahmadinejad put a brave face on hardships resulting from the nuclear policies, telling a German newspaper that economic pressures faced by Europeans were today “more intense than the pressure on the Iranian people.”